1. Field of the Invention
The present invention relates to a method of growing a III-V group compound semiconductor by using liquid phase epitaxial growth, and in particular, to liquid phase epitaxial growth of lattice matched aluminum-indium-arsenide (Al.sub.x In.sub.1-x As) crystal and aluminum-gallium-indium-arsenide (Al.sub.x Ga.sub.y In.sub.1-x-y As) crystal onto indium phosphide (InP) crystal.
2. Description of Prior Art
The aluminum-indium-arsenide compound (Al.sub.x In.sub.1-x As) crystal realizes the lattice matching of the indium phosphide compound (InP) crystal, when x=0.48 and its forbidden band gap is about 1.45 eV which is larger than that (about 1.35 eV) of InP.
Therefore, when the Al.sub.0.48 In.sub.0.52 As crystal is used in place of the conventional InP crystal, or together therewith, as the carrier confining layer of a semiconductor light emitting device (where the InP crystal is used as a substrate and, for example, the indium-gallium-arsenic-phosphide (InGaAsP) or indium-gallium-arsenide (InGaAs) crystal is used as an active layer) or as the window layer of a semiconductor photo detector device (where these crystals are used as the photo absorbing layer), it is expected that the performance of these photo semiconductor devices will improve.
Moreover, the AlInAs has a Schottky barrier height which is larger than that of, for example, InP or InGaAs, which suggest the possibility of its application as a Schottky gate field effect transistor, etc.
Meanwhile, an aluminum-gallium-indium-arsenide compound (Al.sub.x Ga.sub.y In.sub.1-x-y As) crystal is capable of realizing lattice matching to the InP crystal, when it is formed of a composition having the requirements: 0&lt;x&lt;0.48, 0&lt;y&lt;0.47; and its forbidden band gap is from about 0.74 to 1.45 eV.
This forbidden band gap is wider than that of about 0.74 to 1.35 eV for a composition which realizes lattice matching between the InGaAsP crystal and InP crystal; and accordingly, the Al.sub.0.48 In.sub.0.52 As and Al.sub.x Ga.sub.y In.sub.1-x-y As crystals have been anticipated as useful for wide application. For example, a light emitting device which emits the light in the wavelength of 0.85 .mu.m to 1.68 .mu.m or a photo detector device having photo sensitivity within this range may be obtained by combining Al.sub.0.48 In.sub.0.52 As and Al.sub.x Ga.sub.y In.sub.1-x-y As.
In regard to the hetero epitaxial growth of the Al.sub.0.48 In.sub.0.52 As crystal on the InP crystal plane, an example using molecular beam epitaxial growth method has been already proposed. Also, the liquid phase epitaxial growth method was proposed by an inventor of this application in the Appl. Phys. Lett., Vol. 41, No. 2, pages 194-6 (1982). In addition, liquid phase epitaxial growth of Al.sub.x Ga.sub.y In.sub.1-x-y As crystal on the InP crystal plane is also proposed by an inventor of this application in the J. Crystal Growth, Vol. 54, page 232 (1981). In these examples of the epitaxial growth on the InP crystal of the AlInAs or GaInAs crystals, the crystal is grown on the (100) plane of InP crystal. However, when these crystals, particularly when AlInAs is formed by the liquid phase epitaxial growth on the (100) crystal plane of InP, many crystal defects reaching the surface of AlInAs layer are generated, which can be seen in a microphotograph.
The cause of such crystal defects believed to be because of the following: Intrinsically, a three-element liquid of Al-In-As or four-element liquid of Al-Ga-In-As which are growth liquids of these crystals is not equilibrated with the two-element solid phase InP crystal. Moreover, it is difficult to super cool these growth liquids, and therefore, the InP crystal is easily soluble into these growth liquids. On the other hand, the atomic fraction of Al, X.sub.Al.sup.l, in these growth liquids is usually as small as 5.times.10.sup.-4 to 8.times.10.sup.-4 ; and the AlInAs or AlGaInAs crystal shows a low crystal growth rate, particularly when the composition ratio of Al is large. For example, about three minutes is required for liquid phase growth of 0.1 .mu.m of the AlInAs at a temperature of 780.degree. C.
Therefore, a crystal such as AlInAs gradually increases its thickness after the InP crystal is placed in contact with these growth liquids, and the InP crystal dissolves into the liquid. In particular, a deflective area such as a dislocated part quickly dissolves, which expands the defective area, thereby causing many defects to occur when the AlInAs or AlGaInAs crystals are grown on the InP crystal.
It is believed that raising, for example, the growth temperature, is a means for promoting crystal growth of AlInAs, etc. However, if a growth temperature is increased, decomposition of phosphorus (P) from the InP crystal is accelerated and defects of the AlInAs crystal are further increased.